1. Technical Field
The present invention relates to a virtual surround technology.
2. Background Art
Surround systems realizing a sound field with greater ambiance by emitting sounds from a plurality of speakers disposed to surround the periphery of a listener according to audio signals of more than 2 channels (multi-channels) have proliferated.
As the number of channels of audio signals used in the surround systems, 5.1 channels including a front center channel (hereinafter referred to as a “Cch”), a low-frequency effect channel (hereinafter referred to as an “LFEch”) for an audio signal including a considerable component of a low frequency band, a surround left channel (hereinafter referred to as an “LSch”), and a surround right channel (hereinafter referred to as an “RSch”) in addition to a front left channel (hereinafter referred to as an “Lch”) and a front right channel (hereinafter referred to as an “Rch”) used in a normal stereo sound field are currently in wide use. Further, the LSch and the RSch are channels of audio signals emitted from the left rear side and the right rear side, respectively.
In recent years, to realize a more natural sound field, the number of channels of audio signals has tended to increase. Thus, for example, 7.1 channels in which two left and right channels for back surround are added to the rear side of the LSch and the RSch of 5.1 channels or 9.1 channels in which two left and right channels for front presence are added to the upper side of the Lch and the Rch of 7.1 channels are being proliferating.
The most orthodox method of realizing a sound field by audio signals of multi-channels is a method of disposing the number of speakers corresponding to the number of channels within a sound space and emitting sounds according to audio signals of the corresponding channels from the speakers. In the case of this method, it is necessary to dispose the multiple speakers within a sound space. Therefore, inconveniences and disadvantages such as high cost, necessity of a space for disposing the speakers, and necessity of connection of multiple cables for transmitting audio signals and supplying power may be caused.
To resolve or alleviate the above-mentioned inconveniences and disadvantages, numerous technologies for virtually obtaining surround effects have been suggested.
For example, Japanese Unexamined Patent Application, First Publication, No. H08-256400 has suggested a structure in which an improvement in the sense of surround is realized while keeping the sense of expansion of an environmental sound or a reverberant sound by generating audio signals of 2 pseudo-channels from a component of a middle frequency band of a Dolby surround signal having no surround information and adding audio signals obtained through phase-reversing the component of a low frequency band of an input signal to the audio signals.
For example, Japanese Patent No. 4655098 discloses a structure in which surround is realized without disposition of speakers on the lateral side or the rear side of a listener by emitting an acoustic beam having directivity from multiple speakers (a speaker array) arrayed on a plane to a wall surface so that an acoustic beam sound reflected from wall surface reaches the listener from the rear side or the lateral side of the listener.
In the structure disclosed in Japanese Patent No. 4655098, an improvement in the sense of surround of a sound of the low frequency band is designed by dividing components of the low frequency band of an input audio signal into a component with high correlation between channels and a component with low correlation between the channels, assigning directivity to the component with the high correlation so that a sound image can be localized in the middle of two left and right woofers, and assigning directivity to the component with the low correlation so that sound images can be localized to the left and right of the two left and right woofers, respectively.
In recent years, there has been a high need to miniaturize speakers used in surround systems. For example, with thinness and large screens of liquid crystal televisions, speakers included in the liquid crystal televisions or disposed under a rack on which the liquid crystal televisions are placed are preferred to be small due to space restrictions.
In widely used dynamic-type speakers, it is difficult to emit a sound of a low frequency band when the size of a vibration plate becomes small. Therefore, to emit the sound of the low frequency band rarely emitted by a mainly used speaker (hereinafter referred to as a “main speaker”), a subwoofer which is a speaker generally having a vibration plate with a size larger than the main speaker and an excellent sound emission capability in the low frequency band is additionally used in many cases.
Since the subwoofer generally has a size larger than that of the main speaker, a user may desire to dispose the subwoofer on the lateral side, the rear side, or the like of a room so that the subwoofer is not unsightly and obstructive. Therefore, wireless subwoofers that wirelessly receive an audio signal are also popular.
According to characteristics of human hearing, it is difficult to perceive localization of a sound of a low frequency band (for example, a band equal to or less than 100 Hz) compared to a sound of a high frequency band. Therefore, in the related art, a subwoofer having a role in emission of a sound of the low frequency band rarely influences localization of a sound in a realized sound field, regardless of a position in a sound space in which the subwoofer is arranged.
However, with the miniaturization of a main speaker, as described above, a frequency band at which the main speaker can emit a sound is narrowed to the high frequency side. Therefore, a bus management process is performed to emit a low frequency band which may not be emitted by the main speaker by complement of the subwoofer. Since the frequency band of a sound emitted from the subwoofer is spread to the high band through the bus management process, the localization of a sound of another channel may be influenced by the subwoofer.
For example, when the subwoofer conventionally having the role in the emission of a sound of a frequency band equal to or less than 100 Hz has a role in emission of a sound of a frequency band equal to or less than 500 Hz, a component of 100 Hz to 500 Hz frequency bands of a sound emitted from the subwoofer may influence the localization of a sound emitted from the main speaker, and thus the localization of the sound may be pulled in the direction of the subwoofer.
As described above, to resolve the inconveniences and disadvantages caused due to the disposition of multiple speakers when surround of multi-channels is realized, there is a need for a system that virtually realizes the surround of the multi-channels.
In the system (hereinafter referred to as a “virtual surround system”) that virtually realizes the surround of the multi-channels, when listening to sounds emitted from fewer speakers than the number of channels, a listener perceives the sounds as if the listener were listening to sounds emitted from nonexistent virtual speakers. As a result, for example, a surround system of multi-channels such as 5.1 channels is virtually realized by a speaker system of 2.1 channels.
Hereinafter, an example of a surround system of 5.1 channels will be described. In a virtual surround system, localization of sounds emitted from virtual speakers, that is, an LSch speaker (hereinafter referred to as an “LSsp”) and an RSch speaker (hereinafter referred to as an “RSsp”) is realized using auditory psychology of a listener. Therefore, the localization of the sounds emitted from the virtual speakers is easily influenced by various external factors such as a positional relation between the speakers and the listener and the state of a sound reverberating from a wall, compared to sounds emitted from real speakers, that is an Lch speaker (hereinafter referred to as an “Lsp”), an Rch speaker (hereinafter referred to as an “Rsp”), and an LFEch subwoofer (hereinafter referred to as an “SW”). That is, the localization of the sounds of the LSch and the RSch is more unstable than the localization of the sounds of the Lch, the Rch, and the LFEch.
Since virtual process sounds, which are virtual sounds for processing the virtual sounds of the LSch and the RSch, are actually emitted from the physically existent Lsp and Rsp, a component of a low frequency band rarely emitted from the main speakers is required to be emitted from the SW. Accordingly, even in the virtual surround system, through the bus management process, the components of the low frequency band in the virtual process sounds of the LSch and the RSch are emitted together with the components of the low frequency band of the real sounds (sounds which the listener perceives and are emitted from the real Lsp and Rsp and emitted from the positions of the Lsp and the Rsp) of the Rch and the Lch and the sound from the LFEch from the SW.
When a main speaker used in a virtual surround system is small in size, an SW used in the virtual surround system is also required to emit sounds of 100 Hz to 500 Hz frequency bands of which the listener perceives the localization. As a result, the sounds of the LSch and the RSch that are perceived as components of the high frequency band are emitted from the virtual speakers, that is, the LSsp and the RSsp, and the component of the low frequency band is emitted from the real SW. In this case, there is the inconvenience that the localization of the LSch and the RSch may be influenced by the sound emitted from the SW, and thus may be pulled to the position of the SW.